This invention relates to rotary cutter assemblies of the type employed in earth boring applications. More particularly, this invention relates to rotary cutter assemblies which employ rotary cone cutters for drilling wells, blast holes and the like.
Rotary cutter assemblies which employ multiple cutters for rotation about multiple axes of rotation in cooperating fashion to drill earth and hard rock formations are well-known. Many such cutter assemblies employ bit assemblies having legs or connector structures which carry the rotary cutters. The cutter assemblies may also provide means for conducting a flushing fluid from the drill string through the cutter assembly to the bottom of the drill hole. Naturally, the intense work environment of the rotary cutter assembly dictates that the assemblies be constructed in a manner which produces a high degree of structural integrity. Consequently, the connector structures and cutters are commonly pre-assembled at a manufacturing location and are permanently welded together to provide a rotary cutter assembly of an integral form which is then coupled to the drill string of the drill rig.
In the environment to which the rotary cutter assembly of the present invention is ordinarily subjected, frequent replacement of the rolling cutters is common due to the harsh conditions produced by dirt, dust, shock, heat and vibration. During drilling operations the cuttings are commonly blasted against the cutter assembly resulting in pitting, cavitation and other adverse structural damage which ordinarily significantly shortens the useful life of the cutter assembly. Disproportionate wear to one of the multiple rotary cutters or breakage of one of the rotary cutters may effectively disable the entire rotary cutter assembly--especially in light of the fact that the rotary multiple cutters operate in a cooperative fashion. A principal aim of the present invention is to enhance the durability characteristics of a multiple cutter assembly for extending the useful life of the rotary cutter assembly as well as to provide a rotary cutter assembly which permits the replacement of one of the rotary cutters without requiring the replacement of the entire assembly.
A number of rotary cutter assemblies have incorporated features which provide a high degree of structural integrity while also providing for relatively easy replacement of one of the multiple rotary cutters if required. For example, in U.S. Pat. No. 4,335,794 issued to Robert D. Goodfellow, the inventor herein, and entitled "ROTARY CUTTER", a multi-cone roller bit is disclosed wherein the rotary cone cutter is provided with individual releasable legs that permit replacement of a single defective roller cutter unit without requiring that the entire rotary cutter assembly be replaced. All of the releasable legs of U.S. Pat. No. 4,335,794 are clamped to a pot member by a single plug member so that all the rotary cutter units are essentially clamped in place or are released substantially simultaneously. In U.S. patent application Ser. No. 580,368 filed Feb. 15, 1984 by the inventor herein and entitled "ROTARY CUTTER ASSEMBLY", an improved rotary cutter assembly employs a lock sleeve which connects transverse fluid passageways of the drill head and the bit assembly for releasably securing each rotary cutter bit assembly to the drill head. Transverse locking means in the form of pins which are received in complementary slots parallel to the rotational axis of the rotary cutter assembly are also employed to secure the bit assemblies to the drill head. The present invention incorporates new and improved means for securing the cutter bit assemblies to a drill head to provide a multiple bit rotary cutter assembly having enhanced durability characteristics and an extended useful life.